Under ControlMaster, the PID you see is not the tunnel

With ControlMaster auto, which process holds an ssh -L listener depends on how the connection started (tested OpenSSH 10.0p1). ssh -f -N -L ... host started first becomes the master but keeps its '-L' argv, so ps can't tell you that killing it drops every muxed session (they exit 255). With ControlPersist plus a non -N command (ssh -L ... host cmd), the forward lives in a forked ssh: <ControlPath> [mux] process: killing the visible '-L' client leaves the port open. Ask the mux instead: ssh -O check host prints the master PID; ssh -O cancel -L <spec> host drops one forward without touching the master; -o ControlMaster=no -o ControlPath=none gives a tunnel you can kill independently. To find the real owner of a port, map /proc/net/tcp inode to /proc/*/fd.